cmd/compile: fix various small bugs related to type lists

Fix various small bugs related to delaying transformations due to type
params. Most of these relate to the need to delay a transformation when
an argument of an expression or statement has a type parameter that has
a structural constraint. The structural constraint implies the operation
should work, but the transformation can't happen until the actual value
of the type parameter is known.

 - delay transformations for send statements and return statements if
   any args/values have type params.

 - similarly, delay transformation of a call where the function arg has
   type parameters. This is mainly important for the case where the
   function arg is a pure type parameter, but has a structural
   constraint that requires it to be a function. Move the setting of
   n.Use to transformCall(), since we may not know how many return
   values there are until then, if the function arg is a type parameter.

 - set the type of unary expressions from the type2 type (as we do with
   most other expressions), since that works better with expressions
   with type params.

 - deal with these delayed transformations in subster.node() and convert
   the CALL checks to a switch statement.

 - make sure ir.CurFunc is set properly during stenciling, including
   closures (needed for transforming return statements during
   stenciling).

New test file typelist.go with tests for these cases.

Change-Id: I1b82f949d8cec47d906429209e846f4ebc8ec85e
Reviewed-on: https://go-review.googlesource.com/c/go/+/305729
Trust: Dan Scales <danscales@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Dan Scales <danscales@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

src/cmd/compile/internal/noder/expr.go

@@ -164,7 +164,7 @@ func (g *irgen) expr0(typ types2.Type, expr syntax.Expr) ir.Node {
 
 	case *syntax.Operation:
 		if expr.Y == nil {
-			return Unary(pos, g.op(expr.Op, unOps[:]), g.expr(expr.X))
+			return Unary(pos, g.typ(typ), g.op(expr.Op, unOps[:]), g.expr(expr.X))
 		}
 		switch op := g.op(expr.Op, binOps[:]); op {
 		case ir.OEQ, ir.ONE, ir.OLT, ir.OLE, ir.OGT, ir.OGE:
@@ -236,7 +236,7 @@ func (g *irgen) selectorExpr(pos src.XPos, typ types2.Type, expr *syntax.Selecto
 
 			if havePtr != wantPtr {
 				if havePtr {
-					x = Implicit(Deref(pos, x))
+					x = Implicit(Deref(pos, x.Type().Elem(), x))
 				} else {
 					x = Implicit(Addr(pos, x))
 				}

src/cmd/compile/internal/noder/helpers.go

@@ -149,9 +149,13 @@ func Call(pos src.XPos, typ *types.Type, fun ir.Node, args []ir.Node, dots bool)
 		}
 	}
 
-	n.Use = ir.CallUseExpr
+	if fun.Type().HasTParam() {
-	if fun.Type().NumResults() == 0 {
+		// If the fun arg is or has a type param, don't do any extra
-		n.Use = ir.CallUseStmt
+		// transformations, since we may not have needed properties yet
+		// (e.g. number of return values, etc). The type param is probably
+		// described by a structural constraint that requires it to be a
+		// certain function type, etc., but we don't want to analyze that.
+		return typed(typ, n)
 	}
 
 	if fun.Op() == ir.OXDOT {
@@ -191,9 +195,9 @@ func Compare(pos src.XPos, typ *types.Type, op ir.Op, x, y ir.Node) ir.Node {
 	return n
 }
 
-func Deref(pos src.XPos, x ir.Node) *ir.StarExpr {
+func Deref(pos src.XPos, typ *types.Type, x ir.Node) *ir.StarExpr {
 	n := ir.NewStarExpr(pos, x)
-	typed(x.Type().Elem(), n)
+	typed(typ, n)
 	return n
 }
 
@@ -288,17 +292,22 @@ func Slice(pos src.XPos, typ *types.Type, x, low, high, max ir.Node) ir.Node {
 	return n
 }
 
-func Unary(pos src.XPos, op ir.Op, x ir.Node) ir.Node {
+func Unary(pos src.XPos, typ *types.Type, op ir.Op, x ir.Node) ir.Node {
 	switch op {
 	case ir.OADDR:
 		return Addr(pos, x)
 	case ir.ODEREF:
-		return Deref(pos, x)
+		return Deref(pos, typ, x)
 	}
 
-	typ := x.Type()
 	if op == ir.ORECV {
-		typ = typ.Elem()
+		if typ.IsFuncArgStruct() && typ.NumFields() == 2 {
+			// Remove the second boolean type (if provided by type2),
+			// since that works better with the rest of the compiler
+			// (which will add it back in later).
+			assert(typ.Field(1).Type.Kind() == types.TBOOL)
+			typ = typ.Field(0).Type
+		}
 	}
 	return typed(typ, ir.NewUnaryExpr(pos, op, x))
 }

src/cmd/compile/internal/noder/stencil.go

@@ -270,6 +270,7 @@ func (g *irgen) genericSubst(newsym *types.Sym, nameNode *ir.Name, targs []ir.No
 	newf.Nname.Func = newf
 	newf.Nname.Defn = newf
 	newsym.Def = newf.Nname
+	ir.CurFunc = newf
 
 	assert(len(tparams) == len(targs))
 
@@ -286,7 +287,6 @@ func (g *irgen) genericSubst(newsym *types.Sym, nameNode *ir.Name, targs []ir.No
 	for i, n := range gf.Dcl {
 		newf.Dcl[i] = subst.node(n).(*ir.Name)
 	}
-	newf.Body = subst.list(gf.Body)
 
 	// Ugly: we have to insert the Name nodes of the parameters/results into
 	// the function type. The current function type has no Nname fields set,
@@ -305,6 +305,11 @@ func (g *irgen) genericSubst(newsym *types.Sym, nameNode *ir.Name, targs []ir.No
 	newf.Nname.SetTypecheck(1)
 	// TODO(danscales) - remove later, but avoid confusion for now.
 	newf.Pragma = ir.Noinline
+
+	// Make sure name/type of newf is set before substituting the body.
+	newf.Body = subst.list(gf.Body)
+	ir.CurFunc = nil
+
 	return newf
 }
 
@@ -396,6 +401,12 @@ func (subst *subster) node(n ir.Node) ir.Node {
 					as := m.(*ir.AssignOpStmt)
 					transformCheckAssign(as, as.X)
 
+				case ir.ORETURN:
+					transformReturn(m.(*ir.ReturnStmt))
+
+				case ir.OSEND:
+					transformSend(m.(*ir.SendStmt))
+
 				default:
 					base.Fatalf("Unexpected node with Typecheck() == 3")
 				}
@@ -435,38 +446,55 @@ func (subst *subster) node(n ir.Node) ir.Node {
 
 		case ir.OCALL:
 			call := m.(*ir.CallExpr)
-			if call.X.Op() == ir.OTYPE {
+			switch call.X.Op() {
+			case ir.OTYPE:
 				// Transform the conversion, now that we know the
 				// type argument.
 				m = transformConvCall(m.(*ir.CallExpr))
-			} else if call.X.Op() == ir.OCALLPART {
+
+			case ir.OCALLPART:
 				// Redo the transformation of OXDOT, now that we
 				// know the method value is being called. Then
 				// transform the call.
 				call.X.(*ir.SelectorExpr).SetOp(ir.OXDOT)
 				transformDot(call.X.(*ir.SelectorExpr), true)
 				transformCall(call)
-			} else if call.X.Op() == ir.ODOT || call.X.Op() == ir.ODOTPTR {
+
+			case ir.ODOT, ir.ODOTPTR:
 				// An OXDOT for a generic receiver was resolved to
 				// an access to a field which has a function
 				// value. Transform the call to that function, now
 				// that the OXDOT was resolved.
 				transformCall(call)
-			} else if name := call.X.Name(); name != nil {
+
-				switch name.BuiltinOp {
+			case ir.ONAME:
-				case ir.OMAKE, ir.OREAL, ir.OIMAG, ir.OLEN, ir.OCAP, ir.OAPPEND:
+				name := call.X.Name()
-					// Transform these builtins now that we
+				if name.BuiltinOp != ir.OXXX {
-					// know the type of the args.
+					switch name.BuiltinOp {
-					m = transformBuiltin(call)
+					case ir.OMAKE, ir.OREAL, ir.OIMAG, ir.OLEN, ir.OCAP, ir.OAPPEND:
-				default:
+						// Transform these builtins now that we
-					base.FatalfAt(call.Pos(), "Unexpected builtin op")
+						// know the type of the args.
+						m = transformBuiltin(call)
+					default:
+						base.FatalfAt(call.Pos(), "Unexpected builtin op")
+					}
+				} else {
+					// This is the case of a function value that was a
+					// type parameter (implied to be a function via a
+					// structural constraint) which is now resolved.
+					transformCall(call)
 				}
 
-			} else if call.X.Op() != ir.OFUNCINST {
+			case ir.OCLOSURE:
-				// A call with an OFUNCINST will get typechecked
+				transformCall(call)
+
+			case ir.OFUNCINST:
+				// A call with an OFUNCINST will get transformed
 				// in stencil() once we have created & attached the
 				// instantiation to be called.
-				base.FatalfAt(call.Pos(), "Expecting OCALLPART or OTYPE or OFUNCINST or builtin with CALL")
+
+			default:
+				base.FatalfAt(call.Pos(), fmt.Sprintf("Unexpected op with CALL during stenciling: %v", call.X.Op()))
 			}
 
 		case ir.OCLOSURE:
@@ -491,17 +519,22 @@ func (subst *subster) node(n ir.Node) ir.Node {
 			newfn.OClosure = m.(*ir.ClosureExpr)
 
 			saveNewf := subst.newf
+			ir.CurFunc = newfn
 			subst.newf = newfn
 			newfn.Dcl = subst.namelist(oldfn.Dcl)
 			newfn.ClosureVars = subst.namelist(oldfn.ClosureVars)
-			newfn.Body = subst.list(oldfn.Body)
-			subst.newf = saveNewf
 
 			// Set Ntype for now to be compatible with later parts of compiler
 			newfn.Nname.Ntype = subst.node(oldfn.Nname.Ntype).(ir.Ntype)
 			typed(subst.typ(oldfn.Nname.Type()), newfn.Nname)
 			typed(newfn.Nname.Type(), m)
 			newfn.SetTypecheck(1)
+
+			// Make sure type of closure function is set before doing body.
+			newfn.Body = subst.list(oldfn.Body)
+			subst.newf = saveNewf
+			ir.CurFunc = saveNewf
+
 			subst.g.target.Decls = append(subst.g.target.Decls, newfn)
 		}
 		return m

src/cmd/compile/internal/noder/stmt.go

@@ -42,6 +42,12 @@ func (g *irgen) stmt(stmt syntax.Stmt) ir.Node {
 		return x
 	case *syntax.SendStmt:
 		n := ir.NewSendStmt(g.pos(stmt), g.expr(stmt.Chan), g.expr(stmt.Value))
+		if n.Chan.Type().HasTParam() || n.Value.Type().HasTParam() {
+			// Delay transforming the send if the channel or value
+			// have a type param.
+			n.SetTypecheck(3)
+			return n
+		}
 		transformSend(n)
 		n.SetTypecheck(1)
 		return n
@@ -118,6 +124,14 @@ func (g *irgen) stmt(stmt syntax.Stmt) ir.Node {
 		return ir.NewGoDeferStmt(g.pos(stmt), g.tokOp(int(stmt.Tok), callOps[:]), g.expr(stmt.Call))
 	case *syntax.ReturnStmt:
 		n := ir.NewReturnStmt(g.pos(stmt), g.exprList(stmt.Results))
+		for _, e := range n.Results {
+			if e.Type().HasTParam() {
+				// Delay transforming the return statement if any of the
+				// return values have a type param.
+				n.SetTypecheck(3)
+				return n
+			}
+		}
 		transformReturn(n)
 		n.SetTypecheck(1)
 		return n

src/cmd/compile/internal/noder/transform.go

@@ -144,8 +144,10 @@ func transformCall(n *ir.CallExpr) {
 
 	typecheckaste(ir.OCALL, n.X, n.IsDDD, t.Params(), n.Args)
 	if t.NumResults() == 0 {
+		n.Use = ir.CallUseStmt
 		return
 	}
+	n.Use = ir.CallUseExpr
 	if t.NumResults() == 1 {
 		n.SetType(l.Type().Results().Field(0).Type)
 

test/typeparam/typelist.go

@@ -0,0 +1,64 @@
+// compile -G=3
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file tests type lists & structural constraints.
+
+package p
+
+// Assignability of an unnamed pointer type to a type parameter that
+// has a matching underlying type.
+func _[T interface{}, PT interface{type *T}] (x T) PT {
+    return &x
+}
+
+// Indexing of generic types containing type parameters in their type list:
+func at[T interface{ type []E }, E any](x T, i int) E {
+        return x[i]
+}
+
+// A generic type inside a function acts like a named type. Its underlying
+// type is itself, its "operational type" is defined by the type list in
+// the tybe bound, if any.
+func _[T interface{type int}](x T) {
+	type myint int
+	var _ int = int(x)
+	var _ T = 42
+	var _ T = T(myint(42))
+}
+
+// Indexing a generic type which has a structural contraints to be an array.
+func _[T interface { type [10]int }](x T) {
+	_ = x[9] // ok
+}
+
+// Dereference of a generic type which has a structural contraint to be a pointer.
+func _[T interface{ type *int }](p T) int {
+	return *p
+}
+
+// Channel send and receive on a generic type which has a structural constraint to
+// be a channel.
+func _[T interface{ type chan int }](ch T) int {
+	// This would deadlock if executed (but ok for a compile test)
+	ch <- 0
+	return <- ch
+}
+
+// Calling of a generic type which has a structural constraint to be a function.
+func _[T interface{ type func() }](f T) {
+	f()
+	go f()
+}
+
+// Same, but function has a parameter and return value.
+func _[T interface{ type func(string) int }](f T) int {
+	return f("hello")
+}
+
+// Map access of a generic type which has a structural constraint to be a map.
+func _[V any, T interface { type map[string]V }](p T) V {
+	return p["test"]
+}